It takes far more fertilizer and irrigation to produce food for mass-produced meat. Well-maintained pasture has diverse plants year round soaking up a small amount of CO2 versus land for corn that is plowed under. And land for ethical meat often has trees to shade the animals. Mass-produced meat requires highly intensive cleaning of stalls. And for things like beef, it is still unclear whether one diet or another produces more methane, which is a huge portion of the climate impact.
Then there are things like what is done with the manure. In a well-managed factory farm, it is digested. But there are tons of stories about polluted rivers near factory farms that make it clear that often isn't the case. Those polluted rivers result in algal blooms, which is a whole other matter.
Basically, a statement like "more resources to ethically produce meat" confuses the price to a farmer of producing meat with a calculation that incorporates all the externalities, which is a whole lot less clear.
What? It is pretty clear cut that humans eating plants directly requires growing a lot less plants than humans eating meat, which ate those plants. Animals don't grow on sunlight, so they are basically a reactor for turning plants from one type of food into another. And the laws of thermodynamics tell us they aren't 100% efficient, so... eating meat requires more plants to be grown than eating plants themselves...
Had the herbivores been harvested from the wild this would all be true. In practice the herbivores are fed not just grass but beans, grains and other produce. Which has to be grown just like the vegetables eaten by vegetarians. Since the 'conversion factor' - the efficiency by which an animal transforms 1 kg of fodder into 1 kg of edible animal - varies from about 2 (insects) via 5-7 (chicken) via 9-11 (pig) to 14-18 (cow) it becomes clear that it takes a lot more grains, beans and such to feed a carnivore than it takes to feed a vegetarian.